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Cc:     Rafael David Tinoco <rafael.tinoco@linaro.org>, broonie@kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, minchan@kernel.org, ngupta@vflare.org,
        sergey.senozhatsky.work@gmail.com
Subject: Re: [PATCH v2] mm/zsmalloc.c: Fix zsmalloc 32-bit PAE support
To:     linux@armlinux.org.uk
References: <20181025134344.GZ30658@n2100.armlinux.org.uk>
 <20181121001150.405-1-rafael.tinoco@linaro.org>
From:   Rafael David Tinoco <rafael.tinoco@linaro.org>
Organization: Linaro
Message-ID: <91776bf8-0d12-1cc4-1ffb-ca3c486aeb0b@linaro.org>
Date:   Tue, 20 Nov 2018 22:18:40 -0200
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On 11/20/18 10:11 PM, Rafael David Tinoco wrote:
> On 32-bit systems, zsmalloc uses HIGHMEM and, when PAE is enabled, the
> physical frame number might be so big that zsmalloc obj encoding (to
> location) will break, causing:
> 
> BUG: KASAN: null-ptr-deref in zs_map_object+0xa4/0x2bc
> Read of size 4 at addr 00000000 by task mkfs.ext4/623
> CPU: 2 PID: 623 Comm: mkfs.ext4 Not tainted 4.19.0-rc8-00017-g8239bc6d3307-dirty #15
> Hardware name: Generic DT based system
> [<c0418f7c>] (unwind_backtrace) from [<c0410ca4>] (show_stack+0x20/0x24)
> [<c0410ca4>] (show_stack) from [<c16bd540>] (dump_stack+0xbc/0xe8)
> [<c16bd540>] (dump_stack) from [<c06cab74>] (kasan_report+0x248/0x390)
> [<c06cab74>] (kasan_report) from [<c06c94e8>] (__asan_load4+0x78/0xb4)
> [<c06c94e8>] (__asan_load4) from [<c06ddc24>] (zs_map_object+0xa4/0x2bc)
> [<c06ddc24>] (zs_map_object) from [<bf0bbbd8>] (zram_bvec_rw.constprop.2+0x324/0x8e4 [zram])
> [<bf0bbbd8>] (zram_bvec_rw.constprop.2 [zram]) from [<bf0bc3cc>] (zram_make_request+0x234/0x46c [zram])
> [<bf0bc3cc>] (zram_make_request [zram]) from [<c09aff9c>] (generic_make_request+0x304/0x63c)
> [<c09aff9c>] (generic_make_request) from [<c09b0320>] (submit_bio+0x4c/0x1c8)
> [<c09b0320>] (submit_bio) from [<c0743570>] (submit_bh_wbc.constprop.15+0x238/0x26c)
> [<c0743570>] (submit_bh_wbc.constprop.15) from [<c0746cf8>] (__block_write_full_page+0x524/0x76c)
> [<c0746cf8>] (__block_write_full_page) from [<c07472c4>] (block_write_full_page+0x1bc/0x1d4)
> [<c07472c4>] (block_write_full_page) from [<c0748eb4>] (blkdev_writepage+0x24/0x28)
> [<c0748eb4>] (blkdev_writepage) from [<c064a780>] (__writepage+0x44/0x78)
> [<c064a780>] (__writepage) from [<c064b50c>] (write_cache_pages+0x3b8/0x800)
> [<c064b50c>] (write_cache_pages) from [<c064dd78>] (generic_writepages+0x74/0xa0)
> [<c064dd78>] (generic_writepages) from [<c0748e64>] (blkdev_writepages+0x18/0x1c)
> [<c0748e64>] (blkdev_writepages) from [<c064e890>] (do_writepages+0x68/0x134)
> [<c064e890>] (do_writepages) from [<c06368a4>] (__filemap_fdatawrite_range+0xb0/0xf4)
> [<c06368a4>] (__filemap_fdatawrite_range) from [<c0636b68>] (file_write_and_wait_range+0x64/0xd0)
> [<c0636b68>] (file_write_and_wait_range) from [<c0747af8>] (blkdev_fsync+0x54/0x84)
> [<c0747af8>] (blkdev_fsync) from [<c0739dac>] (vfs_fsync_range+0x70/0xd4)
> [<c0739dac>] (vfs_fsync_range) from [<c0739e98>] (do_fsync+0x4c/0x80)
> [<c0739e98>] (do_fsync) from [<c073a26c>] (sys_fsync+0x1c/0x20)
> [<c073a26c>] (sys_fsync) from [<c0401000>] (ret_fast_syscall+0x0/0x2c)
> 
> when trying to decode (the pfn) and map the object.
> 
> That happens because one architecture might not re-define
> MAX_PHYSMEM_BITS, like in this ARM 32-bit w/ LPAE enabled example. For
> 32-bit systems, if not re-defined, MAX_POSSIBLE_PHYSMEM_BITS will
> default to BITS_PER_LONG (32) in most cases, and, with PAE enabled,
> _PFN_BITS might be wrong: which may cause obj variable to overflow if
> frame number is in HIGHMEM and referencing a page above the 4GB
> watermark.
> 
> commit 6e00ec00b1a7 ("staging: zsmalloc: calculate MAX_PHYSMEM_BITS if
> not defined") realized MAX_PHYSMEM_BITS depended on SPARSEMEM headers
> and "fixed" it by calculating it using BITS_PER_LONG if SPARSEMEM wasn't
> used, like in the example given above.
> 
> Systems with potential for PAE exist for a long time and assuming
> BITS_PER_LONG seems inadequate. Defining MAX_PHYSMEM_BITS looks better,
> however it is NOT a constant anymore for x86.
> 
> SO, instead, MAX_POSSIBLE_PHYSMEM_BITS should be defined by every
> architecture using zsmalloc, together with a sanity check for
> MAX_POSSIBLE_PHYSMEM_BITS being too big on 32-bit systems.
> 
> Link: https://bugs.linaro.org/show_bug.cgi?id=3765#c17
> Signed-off-by: Rafael David Tinoco <rafael.tinoco@linaro.org>
> ---
>   arch/arm/include/asm/pgtable-2level-types.h |  2 ++
>   arch/arm/include/asm/pgtable-3level-types.h |  2 ++
>   arch/arm64/include/asm/pgtable-types.h      |  2 ++
>   arch/ia64/include/asm/page.h                |  2 ++
>   arch/mips/include/asm/page.h                |  2 ++
>   arch/powerpc/include/asm/mmu.h              |  2 ++
>   arch/s390/include/asm/page.h                |  2 ++
>   arch/sh/include/asm/page.h                  |  2 ++
>   arch/sparc/include/asm/page_32.h            |  2 ++
>   arch/sparc/include/asm/page_64.h            |  2 ++
>   arch/x86/include/asm/pgtable-2level_types.h |  2 ++
>   arch/x86/include/asm/pgtable-3level_types.h |  3 +-
>   arch/x86/include/asm/pgtable_64_types.h     |  4 +--
>   mm/zsmalloc.c                               | 35 +++++++++++----------
>   14 files changed, 45 insertions(+), 19 deletions(-)

Russel,

I have tried to place MAX_POSSIBLE_PHYSMEM_BITS in the best available 
header for each architecture, considering different paging levels, PAE 
existence, and existing similar definitions. Also, I have only 
considered those architectures already having "sparsemem.h" header.

Would you mind reviewing it ?

Tks
--
Rafael D. Tinoco
Linaro Kernel Validation